In such flame spray process, a wire is passed through a combustion or plasma flame which has relatively high gas velocity characteristics. The wire is melted to form droplets, and the droplets are accelerated by the flame gases exiting a nozzle bore at very high velocity to strike a substrate downstream of and facing the nozzle, whereby the accelerated droplets in striking the surface of the substrate build up a coating thereon. Wire materials are commonly metals such as zinc, aluminum, copper. steel, nickel, stainless steel, and the like.
To date it has been the practice to use single round cylindrical wires. These are readily available and easily fed into the spraying device by a powered roll system feeder. Some systems have been designed to use two or more separate wires fed at different points into a single flame, and although there is an increase in spray rate, a more complex feed system is required.
There is a major disadvantage using single round cross-sectional wires. For a cylindrical structure of this type, a circular cross-section presents the minimum surface area for the flame heat to pass into the metal to effect the necessary heating. Other than round wires may be used such as star shaped, rectangular, etc., but they are more expensive to fabricate and their irregular surface makes them difficult to feed reliably. Patents exemplary of feeding wire in a flame spray system are as follows:
______________________________________ U.S. Pat. No. Issue Date Inventor Title ______________________________________ 4,248,513 Apr. 26, 1966 Sunnen EQUIPMENT FOR FORMING HIGH TEMPERATURE PLASMAS 3,312,566 Apr. 4, 1967 Winzeler et ROD-FEED al. TORCH APPARATUS AND METHOD 4,095,081 June 13, 1978 Ashman ELECTRIC ARC METAL SPRAY- ING DEVICES 4,147,917 Apr. 3, 1979 Jelmorini METHOD AND DEVICE FOR PLASMA-MIG- WELDING 4,370,538 Jan. 25, 1983 Browning METHOD AND APPARATUS FOR ULTRA HIGH VELOC- ITY DUAL STREAM METAL FLAME SPRAYING 4,762,977 Aug. 9, 1988 Browning DOUBLE ARC ARC PREVENTION FOR A TRANSFERRED- FLAME SPRAY SYSTEM 4,788,402 Nov. 29, 1988 Browning HIGH POWER EXTENDED ART PLASMA SPRAY METHOD AND APPARATUS ______________________________________
In U.S. Pat. No. 4,788,402, the embodiment of FIG. 5, two separate material feeds are provided for the flame spray in rod form, fed into the extended arc column at the exit end of nozzle 34. This results in the further increased melt off rate. Plasma spray torches feeding multiple wires into the gas stream initiating the arc therebetween and melting particles from both wires are evidenced by U.S. Pat. No. 4,370,538 at FIG. 6 and U.S. Pat. No. 4,762,977 at FIG. 4. Winzeler et al. U.S. Pat. No. 3,312,566 uses three rods resulting in an increased deposition rate, an increased degree of uniformity and asymmetry in plasma containing the multiple particles. Ashman U.S. Pat. No. 4,095,081 shows two rods fed diametrically opposite to a center plane. Jelmorini U.S. Pat. No. 4,147,917 discloses a simultaneous feeding of two wires where two respective MIG-arcs are struck and maintained between the two welding wires axially introduced into the gas stream and the workpiece W. Such patents exemplify the prior art as known tc the applicant.
It is therefore an object of the present invention to provide an improved flame spray process in which a simplified but highly effective wire feed is achieved using wires of round cross-section with highly increased wire spray rate.